A multi-band camera is an example of an imaging device (e.g. see Patent Document 1). According to an aspect of the multi-band camera, a prism in which a plurality of light refraction planes, having normal lines in different directions with respect to the optical axis of the optical system, is created, is disposed in a position corresponding to an aperture stop of the optical system. By deflecting the plurality of separated luminous flux in different directions respectively using this configuration, object images of the same number as light refraction planes are formed on different image forming positions on an imaging plane for the same object. Different spectral filters, corresponding to the plurality of object images respectively, are disposed immediately after the prism, so that each of the plurality of object images is constituted by predetermined wavelength components. If the plurality of object images constituted by predetermined wavelength components is imaged by a picture element and is image-processed, two-dimensional spectral characteristics of the object can be obtained by a single imaging process.
In such a multi-band camera, the prism is disposed in non-parallel luminous flux, but if the non-parallel luminous flux is deflected by the refraction function of the wedge prism, astigmatism, coma aberration and various other aberrations, including chromatic aberrations caused by the refraction angles which are different depending on the wavelength, are generated, and image quality drops. Furthermore, the projection magnification of the object image is different between the refraction direction and the direction perpendicular to the refraction due to the anamorphic effect by the refraction of the wedge prism, which distorts the object image. Moreover, this distortion generates different optical characteristics depending on a set of a plurality of images, since a plurality of incident planes (refraction planes) of the prims is not parallel, and each luminous flux is deflected in different directions depending on the refraction plane. Therefore if the set of the plurality of images is accurately combined by image processing, different distortion correction processing is required for each set of a plurality of images, which requires more processing. Even if the prism is disposed in parallel luminous flux, problems with chromatic aberrations and distortion of the object image remain, although problems with astigmatism and coma aberration may be solved.
According to an aspect of the multi-band camera, a small lens array is disposed after an intermediate image of the object or immediately after the object image, and a plurality of object images corresponding to a number of small lenses is formed on the image plane. A different spectral filter is disposed in each small lens, and each of the plurality of object images is formed by predetermined wavelength components. The plurality of object images constituted by the predetermined wavelength components is imaged by the picture element and is image-processed, whereby two-dimensional spectral characteristics of the object can be obtained by a single imaging process.
In this multi-band camera, the plurality of object images formed by each small lens in the small lens array has parallax with one another. In the case of disposing the small lens array immediately after the object image, the degree of parallax changes depending on the distance from the object, and these images must be combined by image processing, which requires more processing.
As an aspect of the multi-band camera, a compound eye camera, which uses, as an imaging optical system, only a lens array in which a plurality of lens systems are two-dimensionally arrayed, has been commercialized. In this type of camera, when an object at a near distance is imaged, a difference occurs to the field of view due to major parallax generated among the lenses of the lens array, which makes the edges of the image unusable. A simple method of creating the multi-band camera by arraying a plurality of cameras having identical specifications also has been frequently used, but in the case of this method, focusing must be adjusted for each camera, which is troublesome.